The invention provides a reactor and a process for endothermic gas phase reaction in a reactor.
One example of such a reaction is the conversion of silicon tetrachloride (STC) with hydrogen to trichlorosilane (TCS) and HCl. The conversion of STC with hydrogen to trichlorosilane typically takes place in a reactor at high temperatures, at at least 600° C., ideally at at least 850° C. The relative selectivity is given by the molar proportion of trichlorosilane relative to silicon tetrachloride. It is a measure of how much of the STC used is converted to TCS and thus determines the economic viability of the process.
U.S. Pat. No. 4,536,642 A describes an apparatus and a process for conversion of silicon tetrachloride STC to trichlorosilane TCS.
The reactants are introduced into the vessel through the inlet and brought to temperature with the aid of the hot offgas within the three successive heat exchangers. The heating elements heat the reactants up to the final temperature within the reaction region of the converter. The reaction products are conducted together with the unreacted reactants in a pipe to the heat exchangers before they leave the converter again through the opening. The heat exchangers used consist of graphite.
Both the heating elements and the heat exchangers show an increased level of corrosion, which leads to failure of the reactor. Moreover, the heating elements are subject to greater or lesser corrosion by hydrogen, which can lead in the long term to failure of the reactor.
US 2008/112875 A1 describes a process for conversion of STC to TCS, in which particular attention is paid to the cooling rate of the process gas in the heat exchanger. For the heat exchangers, materials such as SiC, silicon nitride, quartz glass or SiC-coated graphite are used. These materials have the advantage that they react only to a limited degree with hydrogen, for example, and therefore reduce the above-described problems. However, they additionally exhibit the considerable disadvantage that the construction complexity is very high.
US 2013/0287668 A1 discloses a process for hydrogenating chlorosilanes in a reactor, wherein at least two reactant gas streams are introduced separately into a reaction zone, the first reactant gas stream including silicon tetrachloride being conducted through a first heat exchanger unit in which it is heated, and then being conducted through a heating unit, in the course of which it is heated to a first temperature before the first reactant gas stream reaches the reaction zone, and wherein the second reactant gas stream including hydrogen is heated by a second heat exchanger unit to a second temperature, the first temperature being greater than the second temperature, and then being introduced into the reaction zone, such that the mean gas temperature in the reaction zone is between 850° C. and 1300° C., and react to give product gases comprising trichlorosilane and hydrogen chloride, wherein the product gases obtained in the reaction are conducted through said at least two heat exchanger units and preheat the reactant gas streams of the reaction by the countercurrent principle, with flow first through the first heat dewexchanger unit and then through the second heat exchanger unit.
In addition, US 2013/0287668 A1 discloses a reactor for hydrogenation of chlorosilanes, comprising two gas inlet apparatuses through which the reactant gases can be introduced separately into the reactor, and at least one gas outlet apparatus through which a product gas stream can be conducted, at least two heat exchanger units which are connected to one another and which are suitable for heating reactant gases separately by means of the product gases conducted through the heat exchanger units, and a heating zone which is arranged between a first heat exchanger unit and a reaction zone and in which there is at least one heating element.
US 2013/0287668 A1 additionally describes a reactor for hydrogenation of chlorosilanes, comprising a vessel containing a shell face, a lower end and an upper end opposite the lower end, and at least one inlet apparatus for a reactant gas stream and at least one outlet apparatus for a product gas stream, at least one circular heating element or a plurality of heating elements arranged in a circle, at least four cylindrical deflecting devices for gas arranged concentrically in the vessel, suitable for deflecting gas flowing at the upper or lower end of the reactor, the radius of a first cylindrical deflecting device being greater and the radius of the at least three further deflecting devices being less than the radius of the circular heating elements or less than the radius of the circle on which the heating elements are disposed, at least one further inlet device for a reactant gas comprising nozzles mounted in a circle at the lower end of the vessel, the radius of the circle on which the nozzles are disposed being greater than the radius of one of the deflecting devices and less than the radius of a deflecting device adjacent to that deflecting device.
In the prior art, there is inhomogeneous attrition of the heating elements, and there are frequent reactor shutdowns because of failed heating elements. In the course of hydrogenation of chlorosilanes, a reduction in the conversion rate resulting from the failure of heating elements is additionally found.
The objective of the present application arose from these problems.